Method for manufacturing a honeycomb structure having slits

ABSTRACT

A method for manufacturing a honeycomb structure having slits is provided which permits accurate forming of fine slits to cut or grind a targeted cell array alone and which is suitable for application to mass production. The method provides a honeycomb structure having slits and a plurality of arrays of numerous cells aligned in parallel. The slits communicate with an external space and formed along the arrays. The slits are formed by protruding a slit forming member 4-toward the molded article during the extrusion step.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention is directed to a method for manufacturing ahoneycomb structure having slits and having a plurality of rays ofnumerous cells aligned in parallel, an apparatus for manufacturing thesame, and more particularly to a method for manufacturing a honeycombstructure having slits formed along arrays of numerous cells aligned inparallel and communicating with an external space, and an apparatus formanufacturing the same.

2. Related Art Statement

A honeycomb structure is known as a structure in which a plurality ofarrays of numerous cells are formed by being aligned in parallel to abase, and is used as a light yet strong structural member for aircraftor the like, and a catalyst carrier having a large air flow forautomotive exhaust gas purification or the like. Additionally, it isutilized as a dust filter or a solid-liquid separation filter having alarge filtering area per unit volume, in a case where the base is madeof a ceramic porous material having fine pores.

The aforementioned applications are derived from the feature of thehoneycomb structure in that it has a plurality of cells isolated fromexternal space, however, slits communicating with external space areformed on the structure by deliberately cutting or grinding parts of thecells for certain purposes.

For instance, a honeycomb structure 21 shown in FIG. 2(b) is asolid-liquid separation filter for removing insoluble matters of aparticle diameter larger than the pores of a base 22 by injecting aliquid to be treated into cells 23 and by letting only a filtrate thathas passed the pores of the base 22 flow out to external space. A partof the cells 23 is deliberately cut or ground along the specific cellarrays 26 a out of a plurality of cell arrays 26 to form slits 24,thereby the structure can communicate with external space. Such ahoneycomb structure will be referred to hereinafter as a honeycombstructure having slits.

In such a solid-liquid separation filter, as a filtrate having passedthe inside of the base 22, i.e. cells near the central part, flows outdirectly through the slits 24 to external space, the traveling distanceof the filtrate through pores of the base 22 can be shortened to reducethe fluid resistance during filtration. This results in the advantagethat, even where a filter having a large volume is used, the liquidthroughput is not reduced and a sufficient filtering capacity can beretained.

Furthermore, the contamination of the filtrate with a liquid to betreated can be prevented merely by sealing the cell arrays 26 a in whichthe slits 24 are formed at the both ends of said arrays 26 a with asealing member 25 made of glass or the like.

According to the conventional methods, a honeycomb structure havingslits as described above is manufactured by drying and firing ceramicbody after extruding and:

(1) marking off the external side face of the structure in such a mannerthat the specified cell arrays in which slits are to be formed at bothend faces of the honeycomb structure where cell openings are located,are connected with the marked off line, and forming the slits by cuttingor grinding the marked off portions with a micro-grinder, drill or thelike. This method is hereinafter referred to as a first method; or

(2) forming slits by cutting the structure along the specified cellarrays with a grind stone or the like watching with naked eyes todetermine the position of the cell arrays of the honeycomb structure atwhich the slits are to be formed. This method is hereinafter referred toas a second method.

However, in the case of the first method, it is not possible toeliminate machining errors such as breaking arrays of adjacent cells orcutting cell walls of adjacent cells, even cuffing the marked offportions accurately. This is because it is not so easy even forwell-experienced workers to cut or grind the targeted cell arrays alone,in addition to the troublesome manual work of marking off. This isbecause the cell arrays in which slits are to be formed are not alwayspositioned along the lines connecting the cell arrays marked off at theend faces where cell openings are located of the structure due to thefrequent distortion and/or frequent deformation of cell arrays, which isderived from the compression or the deformation of the molded articleduring the steps of extruding, drying and firing the molded article.

That is, the first method is not a simple one fitted for massproduction, and furthermore it is difficult to form fine slitsaccurately.

The difficulty in forming fine slits accurately means that the formationof slits in a honeycomb body of such a fine structure that one havingfine cell pores of 2 to 3 mm and having a wall thickness of about 0.5 mmis extremely difficult.

The second method, on the other hand, can reduce machining errorsbecause slits are formed while watching the cell arrays with naked eyes,compared with the first method. However, there is still a problem sinceit requires such troublesome manual work that one should cut into theend faces of the structure while watching the cell arrays with nakedeyes. Accordingly, one may say that fine slits can be formed accuratelyby utilizing the second method, however, there is a problem in that itis not simple to apply it to mass production.

Moreover, there is another problem in the second method in that themechanical strength at the two ends of the structure is weakenedbecause, inevitably, slits are formed there. The weakened mechanicalstrength at the two ends of the structure is not preferable. This isbecause the filter is easily broken by mechanical forces such asdistortion or impact given thereto at the time of fitting; and thebending stress derived from the dimensional tolerance of the structureor the surface pressure of sealing, in the case that one uses thestructure as a solid-liquid separation filter by utilizing both ends ofthe structure as a sealing portion at the time of fixing it at bothends.

Moreover, the formation of the slits is no an easy task in either thefirst method and the second method since a honeycomb structure hardenedand densified after firing should be used for the processing of theslits in both methods. The second method may be applied to a moldedarticle before drying and firing, however, it is not preferable sincethere is a fear of magnifying the contraction or deformation of thestructure at the two ends at the time of drying and firing. This mightcause sealing failure when the structure is used as a solid-liquidseparation filter.

As hitherto described, any conventional method for manufacturing ahoneycomb structure having slits is not satisfactory since it isfurnished with neither formation of slits in accuracy and fineness norsufficient simplicity fitted for mass production.

SUMMARY OF THE INVENTION

The present invention has been made so as to solve those problems. Thatis, the object of the present invention is to provide a method formanufacturing a honeycomb structure having slits capable of formingaccurately fine slits by cutting or grinding the specified cell arraysalone, and being fitted to mass production.

The present invention has been completed, as a result of intensivestudies, based on the findings that those problems mentioned above canbe solved by adopting a slit forming method in which a slit formingmember is protruded during the step of extruding a honeycomb structure.

Thus, according to the present invention, there is provided a method formanufacturing a honeycomb structure having slits and having a pluralityof arrays of numerous cells aligned in parallel; the slits communicatingwith external space and being formed along the cell arrays, wherein theslits are formed during the step of extruding a honeycomb structure byprotruding a slit forming member toward the molded article during thattime.

In the method according to the present invention, slits can be formedduring the extrusion step with the formation of cells, or alternativelythe slits may be formed by cutting the specified arrays after theformation of the cells.

Further in the method according to the present invention, it ispreferable to monitor the position of the molded article during the stepof the extrusion, and to control the actions of the slit forming memberbased on the monitoring.

Further according to the present invention, there is provided anapparatus for manufacturing a honeycomb structure having slits and aplurality of arrays of numerous cells aligned in parallel; the slitscommunicating with external space and being formed along the cellarrays, which comprises an extruder having an extruding die for ahoneycomb structure, and a slit forming member installed near theextruding die and capable of protruding along specified cell arrays of amolded article being extruded in which slits are to be formed.

In the apparatus according to the present invention, the slit formingmember may be arranged so as to protrude either inwardly or outwardlytoward the extruding die. Where the slit forming member is arranged soas to protrude outwardly the extruding die, a J-shaped bit is preferableas a slit forming member.

Further, it is preferable to have monitoring means for monitoring theposition of the molded article being extruded and control means forcontrolling the actions of the slit forming member based on themonitoring data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) show schematic cross sections of a sift part in onepreferred embodiment of a method for manufacturing a honeycomb structurehaving slits according to the present invention, wherein FIG. 1(a) showshow slits are formed only on an external wall portion of a moldedarticle, and FIG. 1(b) shows how slits are formed in the internal of themolded article.

FIGS. 2(a) and 2(b) schematically illustrate a honeycomb structurehaving slits in one mode of implementing the present invention, whereinFIG. 2(a) shows an expanded view of a cell part and FIG. 2(b), aperspective view of the overall shape.

FIG. 3 schematically illustrates a honeycomb structure having slits asanother embodiment of the present honeycomb structure having slits,wherein FIG. 3(a) is a perspective view of the overall shape and FIG.3(b), an expanded view of cell portion.

FIG. 4 schematically illustrates a shape of an extrusion mouth piece.

FIGS. 5(a) through 5(c) schematically illustrate edge shapes of a slitforming member usable for the present apparatus.

FIGS. 6(a) through 6(g) schematically illustrate edge shapes of anotherslit forming member usable for the present apparatus.

FIG. 7 schematically illustrates one embodiment of the presentmanufacturing apparatus.

FIG. 8 schematically illustrates one of monitoring means usable for thepresent apparatus.

FIG. 9 is a schematic sectional view of forming slit portion accordingto one preferred embodiment of the present method for manufacturing ahoneycomb structure having slits.

FIG. 10 illustrates a schematic partial view according to anotherpreferred embodiment of the present method for manufacturing a honeycombstructure having slits.

FIG. 11 is a schematic diagram illustrating a honeycomb structure havingslits manufactured according to the conventional method.

FIGS. 12(a) and 12(b) schematically illustrate heat exchangers, whereinFIG. 12(a) shows a conventional heat exchanger and FIG. 12(b), a heatexchanger using a honeycomb structure having slits obtainable accordingto the present method.

DETAILED DESCRIPTION OF THE INVENTION

The method for manufacturing a honeycomb structure having slitsaccording to the present invention is characterized in that, at the stepof extruding the honeycomb structure, slits are formed by protruding theslit forming member toward the molded article. Fine slits may be formedby cutting or grinding only the targeted cell array or arrays accordingto the present method and this method is a simple one fitted to massproduction. The present invention will be described in detail below.

1. Manufacturing Method

A first feature of the method for manufacturing a honeycomb structurehaving slits according to the present invention is to form slits duringthe step of extruding the honeycomb structure. According to the presentmethod, a relatively soft green molded article is used for the formationof the slits instead of a hardened and densified, dried, and/or firedarticle. The formation of slits may be done simultaneously with theextrusion of a honeycomb structure body, time and labor required formanufacturing a honeycomb structure having slits may be saved, comparedwith separate slit forming method using a dried or a fired articleaccording to the conventional method.

Further, in the case where the slit cell arrays 26 a are to be sealed asshown in FIG. 2(a) according to the present method, the firing of themolded article and that of sealing members 25 may be madesimultaneously. Thus, one may save one step for firing, compared withthe case when slits are formed in a fired article.

Thus, one may say that this method is not only a highly productivemethod, but also a method fitted to mass production.

Even in the first method among the conventional methods, the firing of amolded article and that of sealing members can only be done at the sametime if the cell arrays in which slits are to be formed are sealed priorto firing. In this case, however, it is not preferable since the removalof the chips formed during forming the slits or the like becomesdifficult because the formation of slits is done after sealing.

A second feature of the method for manufacturing a honeycomb structurehaving slits according to the present invention is to form slits byboring slits in a molded article while the molded article is beingextruded.

Since slits are formed either simultaneously with or immediately afterthe formation of the cells of the honeycomb structure, the positionmatching of the slit forming member with the targeted cell array(s)becomes easier according to this method. Thus, the molded article isless susceptible to the impacts of compression or deformation duringextrusion and the drying and firing of the molded article than separateslit forming method after extrusion.

Therefore, it is made possible to accurately form fine slits by cuttingonly the targeted cell array(s), thereby the occurrence of machiningerrors such as breaking adjacent cell arrays or cutting adjacent cellwalls can be reduced. As this method does not involve any troublesomemanual work such as marking off of the external face in the structure orcutting into the end faces of the structure while watching the cellarray(s) with naked eyes, it may be automated and is fitted to massproduction.

A third feature of a method for manufacturing a honeycomb structurehaving slits according to the present invention is to form slits byprotruding a slit forming member toward a molded article during theextruding step.

Slits may be formed even in the central part of the structure accordingto the present method. This is because the formation of slits having anydesired length in any desired position of a structure in its lengthwisedirection may be done by adjusting the position of the molded articleduring the extrusion step and the timing for protruding the slit formingmember.

Therefore, the problem of weakened mechanical strength at the two endsof the structure or increased compression or deformation can be averted,and thus this method may be applicable, with a particular suitableness,to the manufacture of a honeycomb structure having slits for asolid-liquid separation filter.

Incidentally, It is not preferable to fix a slit forming member to theextruding die instead of protruding the silt forming member toward amolded article. This is because slits 34 would be formed all over theexternal circumference of the molded article 32 as illustrated in FIG.3(a). As a consequence, the mechanical strength of the molded article 32is weakened, and breakage during extrusion of a molded article orhandling the molded article or breakage due to stress concentration atthe time of drying or firing becomes inevitable.

In order to accurately form slits in any desired position of thestructure in its lengthwise direction, it is preferable to monitor theposition of the molded article being extruded and control the actions ofthe slit forming member based on monitoring data accordingly.

Specific methods of monitoring the position of the molded article beingextruded include: (1) direct monitoring of the position of the moldedarticle with a sensor or the like, and (2) indirect monitoring bymeasuring and converting any one factors inclusive of the quantity,duration time for extrusion and the like at the time of extruding apuddled ceramic mixture. By controlling the timing of the actions, i.e.protrusion and retracting of the slit forming member according to themonitored position, slits may be accurately formed in any desiredposition of the structure in its lengthwise direction.

In this manufacturing method according to the present invention, theslit forming member may be protruded along the cell array(s) in whichslits are to be formed of the molded article being extruded.

Where the slit forming member is protruded simultaneously with the cellformation of the honeycomb structure, the slit forming member mayconstitute a part of the extruding die, and slits may be formed byextrusion. Where the slit forming member is protruded immediately afterthe cell formation, slits may be formed by cutting specified portion(s)of the molded article being extruded.

Incidentally, while usually a slit forming member is protruded along onecell array and only that cell array is cut or ground, a slit formingmember may as well be protruded along a plurality of mutually adjoiningcell arrays to simultaneously cut or ground the plurality of cellarrays.

In the method for manufacturing a honeycomb structure having slitsaccording to the present invention, the depth of the slits is notparticularly limited, and it may be provided only in the vicinity of theexternal face of the structure or, in some cases, go through thestructure. Further, a plurality of slits can as well be formed in thelengthwise direction of one cell array of the honeycomb structure or innot just one but a plurality of cell arrays.

Although the length of the slits is not particularly limited, the totalslit length in any one cell array should preferably be not more than ⅓of the overall length of the structure in view of mechanical strength.Where a plurality of slits are to be formed in one cell array, it ispreferable to keep the spacing between the respective slits at {fraction(1/10)} of the length of the slit or more.

Further, the length of slits is not necessarily equal, but, forinstance, the length may be short in the internal portion of thestructure and increased in the external portion thereof. Such aconfiguration is useful when the structure is used as a solid-liquidseparation filter, because it enables the filtrate to be efficientlydischarged to external space. This is because, in the case of asolid-liquid separation filter, the amount of the filtrate dischargedthrough slit is increased due to the joining of filtrate from many cellsat a peripheral portion of the structure, while the amount of thefiltrate discharged through slits in the internal portion thereof isless.

2. Manufacturing Apparatus

The method for manufacturing a honey comb structure having slitsaccording to the present invention can be carried out by using anapparatus for manufacturing a honeycomb structure having slits, whichcomprises, an extruder having an extruding die for a honeycombstructure, and a slit forming member arranged in the vicinity of theextruding die and being movable along specified cell array(s) of anextruded article in which slits are to be formed.

(1) Extruder

Generally, an extruder is a molding machine that is provided with anextruder and an extruding die and can consecutively provide a moldedarticle of a desired shape by extruding a molding material charged tothe extruder from the extruding die. For the apparatus according to thepresent invention, there is no limitation regarding the type of theextruder to be used, and a conventional known extruder can be suitablyused such as a single-shaft, double-shaft or multi-shaft screw extruderor a plunger extruder.

The extruding die in the apparatus for manufacturing a honeycombstructure having slits according to the present invention is required tohave an internal wall corresponding to an external shape of a honeycombstructure, and a shape in which cell blocks 48 corresponding to manycells aligned in parallel as shown in FIG. 4. That is, it should have ashape complementary to a honeycomb structure to be extruded. Many cellsare formed since the cell blocks 48 of the die block a molding materialfrom being pushed forward from the back side (not shown) of the dieshown in FIG. 4.

Incidentally, according to the present invention, a puddled mixtureobtained by admixing a mixture comprising a ceramic powder, a binder,and a solvent, and optionally a surface active agent, a plasticizer orthe like is used as a molding material.

(2) Slit Forming Member

The slit forming member in the apparatus for manufacturing a honeycombstructure having slits according to the present invention is a memberfor forming slits in a green molded article which is being extruded.

Therefore, unlike the case when a dried or fired article is to bemachined, a slit forming member to be used for practicing the presentinvention is not required to have a hardness such as a bit onto which ahigh-speed steel edge is brazed or a grind stone to which diamond iselectro-deposited. Indeed, it is not required to be a revolving bodysuch as a grinder or a drill.

It is preferable to install a slit forming member in the vicinity of theextruding die, thereby any impact of compression or deformation at thetime of extrusion or drying or firing of the molded article can beeliminated as much as possible. Furthermore, the positioning of the slitforming member relative to the targeted cell array may be easilyfacilitated.

More specifically, if the configuration is such that the slit formingmember protrudes in the direction in which, out of the cell blocks ofthe extruding die, the cell blocks matching the cell arrays in whichslits are to be formed are arranged in parallel, the positions of thecell arrays and the slits will match each other to enable fine slits tobe accurately formed into the targeted cell array(s) alone.

The slit forming member, as long as it is installed in the vicinity ofthe extruding die, may be disposed so as to protrude either outwardly orinwardly toward the extruding die or even to protrude both outwardly andinwardly in some cases.

Where the slit forming member protrudes outwardly toward the die, theslit forming member functions as a cutting edge, and slits are formed bycutting the specified array(s) after the formation of the cell.

On other hand, in the case where the slit forming member protrudesinwardly toward the die, the slit forming member constitutes a part ofthe extruding die, and it blocks a puddled mixture to be extruded inthat part. As a consequence, slits are formed simultaneously at the timeof extruding a honeycomb structure. In this case, as shown in FIG. 1(a),if the slit forming member 4 is installed at the position where the tipof the slit forming member 4 is in contact with the cell blocks, slitsmay be formed only on the external wall of the honeycomb structure, orif the slit forming member 4 is installed following the cell blocks asshown in FIG. 1(b), slits 5 can be provided not only on the externalwall 3 a of, but also inside the honeycomb structure.

It is preferable that the thickness of the slit forming member is equalto or less than the diameter of the cell pores not so as to break thecell wall with the slit forming member. In a case where a plurality ofadjacent cell arrays are to be cut or ground simultaneously, it ispreferable that the thickness thereof is such a thickness that the cellwall on the outermost row of the honeycomb structure is not brokenthereby.

Since slits are formed in the molded article during the extrusion stepaccording to the present invention, the slit forming member should berigid enough not to yield to the extruding pressure of a puddled mixturefor forming honeycomb structure. This is because, if it is not rigidenough, the slit forming member may yield to the extruding pressure ofthe a puddled mixture and be deformed to invite such machining errors asbreaking the adjacent cell arrays or cutting the cell wall. A honeycombstructure having a long shape in the extruding direction of a moldedarticle such as a rectangular or a square shape is preferable because itmakes the member rigid in that direction.

A manufacturing method according to the present invention allows slitsto be formed in any desired length by appropriately adjusting theposition of the molded article during extrusion and the timing ofprotruding the slit forming member. Thus, there is no need for thelength of the slit forming member and that of the slit to be identical.Therefore, as long as the aforementioned rigidity is secured, apin-shaped slit forming member having no length in the extrudingdirection of the molded article can be used.

Although the edge shape of the slit forming member is not particularlylimited, its sectional shape across the extruding direction of themolded article may be round, rectangular or wedged as illustrated inFIGS. 5(a) through 5(c). Where the edge shape has corners, such as in arectangular or wedged shape, it is preferable to have a taper or roundshape at the corners to prevent them from developing cracks at the slitend when drying or firing the molded article.

Further, preferable tip sectional shapes across the protruding directionof the slit forming member include, as shown in FIGS. 6(a) through 6(d),round, rectangular, semi-annular and wedged shapes.

Incidentally, it is preferable to match a tip sectional shape 41 acrossthe protruding direction of the member to the external circumference ofthe molded article 42 as illustrated in FIG. 6(e), because it wouldenable the edge (tip face) of the slit forming member to cut into themolded article simultaneously, and thereby the shape of the slit ends isformed accurately. Since the slit forming member is protruded toward themolded article being extruded according the present invention, if a tipsectional shape 43 does not match the molded article 42 as shown in FIG.6(f), the part of the edge on the left of the drawing will firstly cutinto the molded article. Therefore, the end of the slits would be formedin a steep shape, and not accurately in the intended shape.

Where the slit forming member is to be installed so as to protrude outof the extruding die, it is preferable that the slit forming member is aJ-shaped bit.

Where the slit forming member is to protrude out of the die, a slit iscut into the molded article being extruded, resulting in the problemthat the generated chip sticks to the slit forming member and therebyincreases the machining resistance of the edge. An increase in themachining resistance of the edge is undesirable because it would distortthe slit shape or break cell wall on both sides of the slits.

Since a J-shaped bit 45 has a hollow part 46 ahead in the extrudingdirection of the molded article as illustrated in FIG. 6(g), this typeof the slit forming member is preferable since the hollow part 46 canscrape and remove chips.

Incidentally, where the slit forming member is to protrude inwardlytoward the die, as it constitutes part of the extruding die and formsslits during extrusion step, no such problem arises.

The slit forming member may as well be installed so as to protrude fromonly one side of the molded article. In this case, however, the greaterlength and the resultant greater flexibility of the slit forming membermight invite distortion of the slit or break the cell walls on bothsides of the slits.

An arrangement to protrude the slit forming member toward inwardlytoward the molded article from both sides of the molded article wouldreduce the risk of this problem, and is also preferable in that theslits formed would then be shorter in the internal portion of thestructure and longer in the external peripheral portion.

Adjustment of the protrusion, retracting and protruding depth of theslit forming member may be done with a hydraulic cylinder or anelectromotive cylinder besides an air cylinder.

To limit the maximum protruding depth of the slit forming member 51, astopper 54 may be provided as illustrated in FIG. 7.

It is preferable for the manufacturing apparatus according to thepresent invention to have monitoring means for monitoring the positionof the molded article being extruded and control means for controllingthe actions of the slit forming member based on the monitoring data,because slits of any desired length could then be formed in any desiredposition in the lengthwise direction of the molded article bycontrolling the actions such as protrusion and retracting of the slitforming member according to the monitored position.

The monitoring means may be a sensor for monitoring the position of themolded article, a sensor for monitoring the extruded volume of a puddledmixture for a honeycomb body or a timer for monitoring the durationperiod of the extrusion of the puddled mixture.

For instance, in case of an apparatus for manufacturing a honeycomb body61 (hereinafter referred to as a manufacturing apparatus) shown in FIG.8, this apparatus can control the movement of the slit forming member soas to protrude the slit forming member according to signals detected bysensors S1 and S3, and retract the member according to signals detectedby sensors S2, based on the result of monitoring the tip position of amolded article with a plurality of sensors S1, S2, S3, and S4consecutively arranged in the direction of extruding the slit formingmember. The manufacturing apparatus 61 can provide a molded article inthe vicinity of each of whose ends slits are formed. After the formingof slits, the extrusion of the puddled mixture is stopped in response toa detection signal from the sensor S5, and the terminal part of themolded article is cut off near a die 63.

3. Objects of Application

The manufacturing method according to the present invention is intendedto use for the manufacture of a honeycomb structure having slits andhaving a plurality of arrays of numerous cells aligned in parallel. Morespecifically, for that of what has a plurality of “arrays of cells” inwhich the many cells in each array are not formed at random, butarranged in parallel in at least one direction of the honeycombstructure when viewed from the cell opening faces of the structure.

As far as the above-mentioned conditions are met, any type of ahoneycomb body may be manufactured by applying the manufacturing methodaccording to the present invention; that is, irrespective of its overallshape, its size, its cell shape, diameter of its cell pore, its spacingof cells (cell wall thickness) or the like, and materials to be used formanufacturing the honeycomb body. For instance, the base can be tubularhaving a circular, square, rectangular or hexagonal sectional shape, andthe material of the base may be selected as appropriate for theparticular purpose out of various ceramic materials including alumina,titania, mullite, zirconia, cordierite, and any mixture of them.

The shape of individual cells, too, can be circular, rectangular,pentagonal or hexagonal, and in some cases even a plurality of cellshapes can be formed in combination by using cell blocks such as the oneillustrated in FIG. 4.

However, it is preferable that the shape of the cells of the cell arraysin which the slits are to be formed is a rectangular shape. This isbecause the slit forming member can move forwards easily along theinternal wall of cells, thereby machining errors such as breakingadjacent cell arrays or cutting cell walls are prevented, in a case of ahoneycomb body having rectangular cells whose internal walls arelinearly configured relative to the protruding direction of the slitforming member.

4. Usage of Honeycomb Structure

A honeycomb structure having slits, as described above, can be usedparticularly suitably as a solid-liquid separation filter. For instance,a solid-liquid separation filter can be produced by drying a greenhoneycomb molded article produced by the manufacturing method accordingto the present invention, firing the resultant after sealing the cellopening faces of the slit-formed cell arrays thereof, and, in case ofneed, forming further ceramic filtering diaphragm on the internal wallsof cells other than the cells in which the slits have been formed bydipping or the like.

A honeycomb structure having slits according to the present inventionmay be usable as a heat exchanger. When the conventional type ofhoneycomb structure is used for preparing a heat exchanger, a pluralityof honeycomb structures are crossing and stacking each other as a block102 to form a heat exchanger 101 by using the cells 105 thereof directlyas a heat path, as is illustrated in FIG. 12(a). However, in case of ahoneycomb structure having slits shown in FIG. 12(b) manufacturedaccording to the present invention, a heat exchanger 103 may beconstituted of only a single body structure by using cell arrays havingslits 104 and being sealed with a sealing member 106 at their ends, andother arrays of cells 105 as crossing heat paths, respectively.

Thus, the manufacturing method according to the present invention isadvantageous in that such a heat exchanger can be integrallymanufactured thereby.

Embodiments

The manufacturing method according to the present invention will bedescribed in further detail with reference to embodiments thereof. Ithas to be noted, however, the present invention is not limited to thefollowing embodiments.

For both the Embodiments and the Comparative example, a puddled mixtureformed by admixing alumina powder of 150 mm in average grain size, anorganic binder and water was used as the molding material.

For extrusion, a plunger extruder was used, and as the extruding die wasused a hollow round one of 180 mm in inside diameter, in whose hollowpart were arranged hexagonal cell blocks of 3 mm in the across flatlength at a 3.6 mm pitch. This extruding die can give a honeycomb moldedarticle in which about 2000 cells are formed. The extrusion length ofthe molded article was set to 1000 mm.

In both the Embodiments and the Comparative example, nine slits wereformed in every sixth cell array at the portion of 30 to 100 mm from thetwo ends of the respective honeycomb structures; all of which wentthrough the respective honeycomb structure. Thus a total of 18 slits(9×2 ends) were formed per honeycomb structure.

1) Machining Errors

The number of machining errors, including breakage of adjacent cellarrays and accidental cutting of cell walls, which occurred during theforming of 18 slits in a honeycomb structure were counted. Each case ofcomplete absence of machining error was marked with ⊚, and one in whichany error was found was marked with ×.

2) Accuracy of Groove Width

For Embodiments 1 through 3, the groove widths of the slits weremeasured after drying the respective molded article in which slits hadbeen formed. For Comparative Example 1, slits were formed into the driedarticle, and the groove widths of the slits were immediately measuredthereafter. Groove widths of not less than 1.5 mm and within 2.5 mm weremarked with ⊚, ones over 2.5 mm or not more than 3.0 mm, with Δ, andothers, with x.

3) Hours Required for Machining

Hours required to form 18 slits in each honeycomb structure weremeasured. Cases taking no extra machining time after the completion ofthe extrusion forming were marked with ⊚, while others that did take anextra machining time after the completion of the extrusion forming wasmarked with x.

Embodiment 1

Slits were formed in a honeycomb structure at to extrusion step, using amanufacturing apparatus 1 shown in FIG. 1(b), which was equipped with aplate 4 having a width of 2.4 mm and a length of 6.7 mm as a slitforming member. The slit forming member was installed so as to protrudewithin an extruding die 2, and from both sides of a molded article 3inwardly toward a molded article 3. The results are shown in Tables 1and 2.

Incidentally, for the manufacturing apparatus of FIG. 1 (b), the slitforming member installed on only one side of the molded article isillustrated for the convenience of the drawing, and the one on the otherside is omitted. The same is true of the manufacturing apparatuses shownin FIGS. 9 through 11, as well.

Embodiment 2

Slits were formed at the extrusion step by using a manufacturingapparatus 71 shown in FIG. 9, equipped with a pin 74 having a diameterof 2.4 mm as a slit forming member. The slit forming members wasinstalled so as to protrude within an extruding die 72, and from bothsides of a molded article 73 inwardly toward a molded article 73. Theresults are shown in Tables 1 and 2.

Embodiment 3

Slits 85 were formed at the extrusion step by using a manufacturingapparatus 81 in FIG. 10, equipped with a J-shaped bit 84 having a widthof 2.4 mm as a slit forming member. The slit forming member wasinstalled so as to protrude outwardly toward an extruding die 82, butfrom both sides of a molded article 83 toward inwardly toward a moldedarticle 83. The results are shown in Tables 1 and 2.

Comparative Example 1

After drying a molded ankle having no slits formed, the external sideface of a honeycomb structure obtained as dried molded article 93 wasmarked with a line by connecting the specified portions of therespective cell arrays in which slits were to be formed at both endfaces where cell openings were located of the structure 93, and slits 95were formed by cutting the marked portions with a grinding stone 94 onwhich diamond was electro-deposited. The results are shown in Tables 1and 2.

TABLE 1 Machining Timing of slit Slit forming method formation memberEmbodiment 1 Protrusion During extrusion Planar Embodiment 2 ProtrusionDuring extrusion Pin Embodiment 3 Cutting During extrusion J-shaped bitComparative Cutting After Grinding stone Example 1 drying/firing

TABLE 2 Machining errors Accuracy of Machining (numbers groove widthtime Tool Overall formed) (mm) (min) durability Workability Costevaluation Embodiment 1 0 ⊚ 1.5- ⊚ 0 ⊚ Long ⊚ Automatic, no ⊚ Low ⊚ ⊚2.0 marking Embodiment 2 0 ⊚ 1.5- ⊚ 0 ⊚ Long ⊚ Automatic, no ⊚ Low ⊚ ⊚2.0 marking Embodiment 3 0 ⊚ 2.0- ⊚ 0 ⊚ Long ⊚ Automatic, no ⊚ Low ⊚ ⊚2.4 marking Comparative 7 x 2.6- Δ 32 x Short x Manual, x High ⊚ xExample 1 3.0 marking required

Results

1) Machining Errors

While no machining error occurred with any of Embodiments 1 through 3,cell walls were accidentally cut in seven positions in ComparativeExample 1.

2) Accuracy of Groove Width

Regarding Embodiments 1 through 3, although a slight contraction of slitwidth was observed after drying Embodiments 1 and 2, there was noproblem in practical use, and the accuracy of groove width wassatisfactory in both cases. In Comparative Example 1, the accidentalcutting of cell walls in some cases almost broke the cell walls, and theaccuracy of groove width was poor.

3) Machining Time

While no extra machining time was taken to form slits in Embodiments 1through 3 because slits were formed simultaneously with extrusion, 32extra minutes were taken for Comparative Example 1 as 18 slits; nineeach in two positions had to be formed while the worker was watching thearticle.

Other Findings

For Comparative Example 1, as slits were formed in a hardened driedarticle, the grinding stone was worn out soon. On the other hand, forEmbodiments 1 through 3, where a green body of a molded article wasmachined in every case, the slit forming member wore long. The planarslit forming member of Embodiment 1 lasted longest, followed by the pinof Embodiment 2 and the J-shaped bit of Embodiment 3 in that order.

Furthermore, while Embodiments 1 through 3 required no particular manualmachining task as an automated manufacturing apparatus formed slits, thework on Comparative Example 1 was troublesome, involving marking on theexternal face of the structure and cutting while directly watching thestructure with naked eyes. Moreover, in case of Comparative Example 1,it required a longer machining time per honeycomb structure, and thetool was quickly out of order. Furthermore, it required a high machiningcost attributable to the troublesome work.

To totally evaluate the above-described individual aspects, whileEmbodiments 1 through 3 gave satisfactory overall results, ComparativeExample 1 involved problems in all respects including machiningaccuracy, machining time, tool durability, workability and cost.

As hitherto described, the manufacturing method and the manufacturingapparatus according to the present invention permit accurate forming offine slits to cut or grind the targeted cell array(s) alone and moreoverare suitably applicable to mass production.

What is claimed is:
 1. A method for manufacturing an extruded honeycombstructure, comprising the steps of: extruding a honeycomb structurehaving a plurality of arrays of cells aligned in parallel; and moving aslit forming member toward and any from said honeycomb structure toengage and disengage a portion of an outer surface of said honeycombstructure during said extruding step to form slits along said arrayswhile said honeycomb structure is extruded; wherein said slitscommunicate with an external space and with an interior of at least onecell of said honeycomb structure.
 2. The method according to claim 1wherein said slits are formed simultaneously with said cells byextrusion.
 3. A method for manufacturing an extruded honeycomb structurehaving slits and a plurality of arrays of numerous cells aligned inparallel, said slits communicating with an external space and with aninterior of at least one cell of said extruded honeycomb structure, saidslits being formed along said arrays; wherein said slits are formedwhile said honeycomb structure is extruded by protruding a slit formingmember toward said honeycomb structure; and wherein the position of saidhoneycomb structure being extruded is monitored during extrusion, andthe actions of said slit forming member are controlled based onmonitoring data.
 4. The method according to claim 3, wherein theposition of said honeycomb structure being extruded is monitored duringextrusion, and the actions of said slit forming member are controlledbased on monitoring data.
 5. A method for manufacturing an extrudedhoneycomb structure having slits and a plurality of arrays of numerouscells aligned in parallel, said slits communicating with an externalspace and with an interior of at least one cell of said extrudedhoneycomb structure, said slits being formed along said arrays; whereinsaid slits are formed during the extrusion process of said honeycombstructure, after fanning said arrays of cells, by protruding a slitforming member toward said honeycomb structure; and wherein the positionof said honeycomb structure being extruded is monitored duringextrusion, and the actions of said slit forming member are controlledbased on monitoring data.